1. Field of the Invention
The present invention relates to an image discriminating apparatus for discriminating the type of an image to be processed in an image processor within an image creating apparatus such as digital color copiers and printers capable of printing in multi-colors. Specifically, the invention relates to an image discriminating apparatus for discriminating ranges in an image in which color areas and monochrome areas might be mixed.
2. Description of the Related Art
Hitherto, image data used for copying or printing images in offices and others has been that of a black-and-white image called a monochrome image in many times and it may be not too much to say that they are mostly monochrome data. However, since color image creating apparatuses such as a high image quality color copier and a color printer are spreading and the needs for printing in color are increasing also in offices lately, images handled in the offices are to be also colored more and more. Accordingly, color images and monochrome images are mixed among images to be processed by the color image creating apparatus.
In such color image creating apparatus, there is a case when black characters and fine lines do not form halftone dots and are blurred due to misregistration of colors and to the spectral and distributive characteristics of inks when a black-and-white image is copied by superimposing a plurality of colors of color recording substances. Further, considering the process in processing a color image, there have been problems that it takes time to process the image as if it is composed of a plurality of color-separated components even though it is a black-and-white image and that it is costly to form the image through a plurality of processes, beside the problem that the copying quality or the printing quality drops as described above. The plurality of components described above are the three primary colors of red (R), green (G) and blue (B) or of yellow (Y), magenta (M) and cyan (C) for example.
Dedicated image processing and image creation are carried out on a color original and a monochrome original, respectively, in order to create color and monochrome images in high quality and efficiently. For instance, as for the color original, an image thereof is created by using toners or inks of a plurality of colors such as Y (yellow), M (magenta), C (cyan) and BK (black) after implementing color data image processing on each pixel data. As for the monochrome original, an image thereof is created by using monochrome or single-color toner or ink after implementing monochrome data image processing on each pixel data. Thereby, the reproducibility of the color original may be improved and it is possible to prevent color toners or the like from being wasted for the monochrome original and color noise from occurring at edge portions of the image.
Accordingly, it is necessary to judge whether an image to be processed is a color image containing color information or a monochrome image composed of only monochrome information and to select an appropriate process corresponding to the type of the image in the color image creating apparatus. Therefore, it is essential to provide, the color image discrimination for judging whether the image is a color image or a monochrome image.
As the prior art technologies concerning on the color image discrimination, there have been ones disclosed in Japanese Unexamined Patent Publications JP-A 3-270380 (1991) and JP-A 4-282968 (1992) for example. JP-A 3-270380 has introduced a method of outputting a color image discriminating signal in correspondence to a number of output times of a color discriminating signal. That is, this prior art method comprises steps of judging whether each pixel is a color pixel or a monochrome pixel, counting a number of color pixels within an image, judging the image as a color image when the counted counter value indicates that the color pixels occur more than a predetermined number of times and judging the image as a monochrome image otherwise.
JP-A 4-282968 has introduced an original discriminating apparatus for discriminating a color image on the basis of a result of discrimination of each line. That is, this prior art apparatus discriminates an image through steps of judging whether each pixel is a color pixel or a monochrome pixel, recognizing detected continuous color pixels as a color block when the existence of the color pixels which continue more than a predetermined number in order of given pixels is detected, judging a line as a color line and counting it when there exist more than a predetermined number of color blocks within that one line, judging the image as a color image when there exist more than a predetermined number of color lines within the image and judging the image as a monochrome image otherwise.
However, the original discriminating apparatus of JP-A 4-282968 described above has had problems that because it performs the judgement whether or not a pixel is a color pixel, the sampling of the color block, the judgement whether or not a line is a color line and the judgment whether or not an image is a color original, respectively, by comparing with a single threshold value set in advance, it can determine whether the image is a color original or a monochrome original only alternatively in the end, it cannot deal with a situation where the final discrimination result may be erroneous like the case when erroneous discrimination occurs in the judgment whether or not a pixel is a color pixel, in the sampling of the color block and in the judgment whether or not a line is a color line, and it cannot judge whether or not the original is a color original accurately. It has had another problem that when reading precision of original reading means is low, it is liable to cause color noise at peripheral or edge portions of black characters of a monochrome original and to discriminate erroneously a monochrome pixel as a color pixel by the color noise.
Further, although the prior art technologies disclosed in JP-A 3-270380 and JP-A 4-282968 judge whether each pixel is a color pixel or a monochrome pixel and discriminate an image by a range occupied by an area composed of color pixels within the image or by a rate between an area composed of color pixels and an area composed of monochrome pixels in the image discrimination. However, in such a method, because no consideration is given to erroneous discrimination of pixels, there has been a possibility that the result of the image discrimination is also erroneously outputted when the erroneous discrimination occurs in the pixel discrimination.
As the erroneous discrimination of pixels, there are cases of erroneously judging a color pixel as a monochrome pixel and vice versa, erroneously judging a monochrome pixel as a color pixel. Such erroneous discrimination results from the effect of the color noise which occurs mainly at the monochrome edge portions and from mishandling of a pixel which cannot be judged whether it is a color pixel or a monochrome pixel just by a value of density of one pixel and which is often questioned at the ground part of the original and in an area of so-called a pastel. The color noise which occurs at the monochrome edge portion is color misregistration which results from deviation in reading an image and a degree of reading. When it occurs, there is a possibility that a pixel which should be actually belonging to a monochrome range is recognized as a color pixel belonging to a color range.